A conventional high-pressure fuel supply pump described in Japanese Patent Laid-Open No. 2004-138062 includes a relief valve mechanism, in which when a fuel thermally expands due to a malfunction of a flow rate control mechanism of an intake valve and a discharge valve or an increase in a temperature of a piping and the like and a pressure in a high-pressure fuel capacity chamber attains an abnormally high pressure, the pressure in the high-pressure fuel capacity chamber is reduced to a predetermined pressure or less, so that the high-pressure fuel injection valve, the piping, and the like are prevented from malfunctioning.
This relief valve mechanism s configured such that a ball valve is pressed onto a relief seat with a biasing force of a spring, and the fuel flows only in one direction from a downstream side to an upstream side of a discharge valve. When a pressure at a downstream side of an output valve becomes more than a set pressure determined by a set load of the spring, the fuel is relieved to the upstream side of the discharge valve. Further, the relief valve mechanism is fixed to a relief path connecting the upstream side of the discharge valve and the downstream side of the discharge valve, and is inserted in an orientation from the upstream side of the discharge valve to the downstream side of the discharge valve.